Generator section of a two-phase flow liquid metal magnetohydrodynamic (LMMHD) generator

Abstract

Two-phase LMMHD energy conversion systems have potentially significant advantages over conventional systems such as higher thermal efficiency and substantial simplicity with lower capital and maintenance costs. Maintenance of low velocity slip is of importance for achieving high generator efficiency. A bubbly flow pattern ensures very low velocity slip. The full governing equations have been written out, and a computer prediction code has been developed to analyze performance of a two-phase flow LMMHD generator and nozzle under conditions of no slip. Three different shapes of an LMMHD generator have been investigated. Electrical power outputs are in the 20 kW range. Generator efficiency exceeds 71 percent at an average void fraction of about 70 percent. This is an appreciable performance for a short generator without insulating vanes for minimizing electrical losses in the end regions.

I claim: 
     
       1. A generator section assembly for use in a liquid metal magnetohydrodynamic electricity generator comprising: a duct for enclosing a two-phase fluid flow, including a liquid metal and a gas, the duct having an inlet and an outlet;   a pair of sidewalls that form two walls of the duct, the distance between the two sidewalls increasing linearly from the inlet towards the outlet;   a pair of electrodes that form two opposing walls of the duct and are positioned for contacting with the two-phase flow, each of the pair of electrodes having a surface region forming a wall of the duct having a shape of a circular arc of radius from the inlet of the duct towards the outlet of the duct to form a duct having a non-linear increase in the distance between the pair of electrodes from the inlet of the duct towards the outlet of the duct, thus providing a non-linear expansion region within the duct as the distance between the pair of electrodes that form a walls of the duct increases non-linearly, the duct thus expanding linearly along one dimension and non-linearly along the other dimension; and   a magnetic field generating means for creating a magnetic field within the two-phase flow to generate electricity as the two-phase flow passes through the magnetic field within the non-linear expansion region of the duct.   
     
     
       2. The generator section assembly according to claim 1 wherein the magnetic field generating means includes a permanent magnet having pole pieces, the pole pieces being positioned adjacent the sidewalls of the duct. 
     
     
       3. The generator section assembly according to claim 2 wherein the distance between the pole pieces increases linearly from the inlet towards the outlet. 
     
     
       4. The generator section assembly according to claim 1 wherein the slope of increase of the distance between the sidewalls is between the range of 1 to 30 and 1 to 50. 
     
     
       5. The generator section assembly according to claim 4 wherein the slope of increase of the distance between the sidewalls is approximately 1 to 40, such that the distance between the sidewalls increases 1 unit of measure when the length increases 40 units of measure. 
     
     
       6. The generator section according to claim 5 wherein the distance between the sidewalls at the inlet is approximately 0.5 centimeters and the distance between he sidewalls at the exit is approximately 1 centimeter for a duct having a length of 22 centimeters. 
     
     
       7. The generator section according to claim 1 wherein the sidewalls include at least two members, a support member and an electrical insulating member, the insulating member being between the support member and the two-phase flow to prevent electrical contact between the liquid metal and sidewall support member. 
     
     
       8. The generator section according to claim 7 wherein each sidewall support member extends as a unitary member from one electrode of the pair to the other electrode of the pair and a bolt extends through one sidewall support member, through one sidewall insulating member, through one electrode of the pair, through the other sidewall insulating member, and through the other sidewall support member to clamp the pair of electrodes between the sidewall support members and form the four walls of the duct. 
     
     
       9. The generator section assembly according to claim 1 wherein each of the pair of electrodes has a shape of a circular arc of radius extending the entire length of the duct from the inlet to the outlet, providing a non-linear expansion region for the entire length of the duct from the inlet to the outlet. 
     
     
       10. The generator section assembly according to claim 1 wherein each of the pair of electrodes has a shape of a circular arc of radius extending from the inlet for only a portion of the duct towards the outlet and having a shape of linear expansion from the arc portion to the end of the duct, providing a non-linear expansion region for only a portion of the duct that is adjacent the inlet and a linear expansion a portion of the duct that is adjacent the outlet. 
     
     
       11. The generator section assembly according to claim 1 further including a nozzle section forward of the generator section, the nozzle section having a decreasing cross-sectional area prior to the inlet of the duct for increasing the speed of a two-phase flow through the inlet of the duct. 
     
     
       12. A duct for use in a electrical generator section comprising: four walls forming the enclosure for the duct;   an inlet region of the duct;   an outlet region of the duct; and   a non-linear expansion of the duct from the inlet to the outlet that is created by the distance between at least two of the walls increasing non-linearly from the inlet towards the outlet, the non-linear expansion of the duct being created by two curving walls of the duct each having a circular arc of radius adjacent the inlet of the duct and the distance between the walls increasing towards the outlet of the duct, the arc of the curvature of the walls being selected such that the shape of the curving walls is an arc that extends along only a portion of the duct and the shape of the curving walls from the end of the arc shape to the outlet of the duct is a linearly increasing shape.   
     
     
       13. The duct according to claim 12 wherein the distance between the other two of the four walls increase linearly from the inlet to the outlet. 
     
     
       14. The duct according to claim 12 further including electrodes positioned for being in contact with the interior of the duct to permit electricity generated with the duct to be transferred outside of the duct. 
     
     
       15. The duct according to claim 14 wherein the curving walls are the electrodes. 
     
     
       16. A generator section assembly for use in a liquid metal magnetohydrodynamic electricity generator comprising: a duct for enclosing a two-phase fluid flow, including a liquid metal and a gas, the duct having an inlet and an outlet;   a first pair of sidewalls that form two walls of the duct; and   a second pair of sidewalls that form two opposing walls of the duct and are positioned for being in contact with the two-phase flow, each of the second pair of sidewalls having a shape of a circular arc of radius for a portion of their length from the inlet of the duct towards the outlet of the duct and an angled region that extends at a selected angle from the end of the arc region to the outlet of the duct to form a duct having a non-linear expansion region for a portion adjacent the inlet and a linear expansion region for a portion adjacent the outlet.   
     
     
       17. The generator assembly according to claim 15 wherein the second pair of sidewalls are electrodes that each extend as a unitary member along the entire length of the duct, the shape of the electrodes being a circular arc of radius for a portion and being a straight, angled shape for a portion. 
     
     
       18. The generator assembly according to claim 17 wherein the distance between the first pair of sidewalls increases linearly from the inlet to the outlet. 
     
     
       19. The generator section according to claim 18 wherein the width of the electrodes increase from the inlet to the outlet. 
     
     
       20. The generator section according to claim 16 further including: a magnetic field generating means for creating a magnetic field within the liquid metal to generate electricity as the liquid metal passes through the magnetic field within the non-linear expansion region of the duct.   
     
     
       21. A generator section assembly for use in a liquid metal magnetohydrodynamic electricity generator comprising: a duct for enclosing a two-phase fluid flow, including a liquid metal and a gas, the duct having an inlet and an outlet;   a pair of sidewalls that form two walls of the duct;   a pair of electrodes that form two opposing walls of the duct and are positioned for contacting with the two-phase flow, each of the pair of electrodes having a surface region forming a wall of the duct having a shape of a circular arc of radius from the inlet of the duct towards the outlet of the duct to form a duct having a non-linear increase in the distance between the pair of electrodes from the inlet of the duct towards the outlet of the duct, thus providing a non-linear expansion region within the duct as the distance between the pair of electrodes that form a walls of the duct increases non-linearly;   a magnetic field generating means for creating a magnetic field within the two-phase flow to generate electricity as the two-phase flow passes through the magnetic field within the non-linear expansion region of the duct; and   a nozzle section forward of the generator section, the nozzle section having a decreasing cross-sectional area prior to the end of the duct for increasing the speed of a two-phase flow through the inlet of the duct.